1. Field of the Invention
This invention relates to improvements in display apparatus for displaying and entering information from and into data processing apparatus such as personal computers. More particularly, the invention relates to an improved pointing device having an array or grid of Hall effect sensors that are actuated by a magnetic actuator and are integrated with a thin film transistor (TFT) liquid crystal display (LCD).
2. Description of Related Art
Touch displays, for data processing systems, combine the output functions of a display with input functions allowing a user to input information into the system. In portable computers, where size and weight are critical, LCDs are the current display of choice among portable computer manufacturers. LCDs are commonly formed with an active matrix of picture elements (PELs) each containing a TFT coupled with liquid crystal material that transmits light in accordance with control signals applied to the TFT. The transmissivity or apparent brightness of the PEL is a function of the polarization of the liquid crystal material which is a function of the magnitude of a drain voltage applied to the TFT and of the time during which such voltage is applied in conjunction with a gate signal.
Adding touch capability to a display usually increases its size and weight. The technologies that exist for incorporating touchscreen capability include resistive, capacitive, surface acoustic wave (SAW), light emitting diode beam, and scanning lasers. These technologies are all packaged separately from the display itself or added as separate layers in the manufacturing process.
Cursor positioning devices, such as keyboard keys, trackballs, joysticks, and mice, have abstractions of use that are not well suited to a natural human interface, and normally require tethers, cables, or boxes. Unless the devices are connected by an infrared or radio frequency link, the cables restrict and interfere with user freedom of movement.
Overlaid pointing devices are affected by problems. A user's finger size can generate false points or cause difficulty in achieving tight control on a point when using resistive, capacitive, or SAW touchscreens. These types of touchscreens are also susceptible to buildup of dirt or grease.
A further problem of parallax is caused by the thicknesses of overlays on the front of displays, in relation to the source of light control, i.e., the LCD matrix itself. Depending on view angle, parallax distortion can cause difficulty in placing the pointing subsystem to the desired locations.
As should be readily apparent from the description below, the invention includes a unique array of Hall effect elements directly integrated into the LCD semiconductor control structure. A Hall effect element is a well known device whose operating characteristics have been described in numerous articles including: Trent Wood, "An introduction to the use of Hall effect devices", Measurement-Control Volume 21, May 1988, pages 109-111; Douglas White, "The Hall effect sensor: operation and application", Australian Electronics Engineering, April 1989, pages 84-88; R. S. Popovic, "Hall-effect devices", Sensors and Actuators, 17(1989), pages 39-53; and S. Kordic, "Integrated Silicon Magnetic field sensors", Sensors and Actuators, 10(1986), pages 347-378. The latter two articles describe how Hall effect devices can be made by integrated circuit techniques. While these articles describe many diverse applications, most if not all involve the use of a single Hall effect device primarily designed to sense the proximity of a magnet having the proper orientation and polarity. None disclose the use of an array of Hall effect devices integrated into an LCD in the manner of the invention.